Electro-Optical SystemsElectro-Optical Systems

The almost last lecture of Weapons Class

What are we talking about?What are we talking about?

• Optically guided weapons• Night vision goggles• Thermal Imaging• Laser Guided Munitions

Learning ObjectivesLearning Objectives

• The student will understand the properties of Infrared radiation.

• The student will understand detector features and their effect on performance.

Electro-Optical SpectrumElectro-Optical Spectrum

• Electro-Optical Band 1011-1016 Hz• Visible ~1015 Hz• Infrared ~1011-1014

Hz

• Portion of the EM spectrum that lies between X-rays and microwaves

Sources of EO Radiation

• Turbojet exhaust, a tank engine, or a person

• Lasers may serve as illuminator for an IR weapon’s guidance

• Man-made artificial illumination (lights, flares, etc)

• Natural sources

Sources (Radiators)Sources (Radiators)• Selective Emitters

– Narrow wavelength band – line spectra– Excitation of individual atoms or

molecules• Thermal

– Continuous spectrum of wavelengths with some max radiated energy at some particular λ

– Radiates in proportion to the absolute temperature (Kelvin).

LasersLasers

• Laser is light – a form of EM radiation

• Light Amplification by Stimulated Emission of Radiation

• Can emit in the ultraviolet, visible, and infrared portions of the spectrum

Lasers – Military Applications• Targeting tool

– Absorbed by target – thermal radiator– Reflected by target – selective radiator

• Modulated– Different lasers of the same frequency to be

deconflicted and limits enemy interference

• Weapon Systems: Hellfire, Maverick, Rockeye

• Stand alone: Laser Range finders, Beam riders, and laser target designators (LTD)

Infrared

• Can not be detected with the human eye

• Passive system that collects thermal radiation emitted from the target.

• Used in military and law enforcement applications.

IR image of a snake eating a mouse

Characteristics of Thermal Energy

• Attenuation – propagation losses primarily through:– Uneven spreading– Absorption– Scattering– Turbulence

• Refractive index fluctuations (Temp, pressure, density)

Detectors

• Photon – Convert absorbed photon energy into

released electrons

• Themal– Absorb energy over a broad band of

wavelengths– Causes tempurature of material to

increase• At least one inherent electrical property

that changes with temperature

Military Uses

• Laser guided munitions– Designated from air or ground

• Thermal homing missiles• Optical Guidance• Night Vision

Night Vision Devices (NVD)

• Low light level image intensifiers• Improve night vision

– Increase amount of light reaching the eye

– Light amplification• NVIS• FLIR

Night Vision Scopes

• “Amplify” existing light• Available light (photons) is

collected and focused on the image intensifier

• Conversion of photon to electron• CAN NOT see in complete dark

– IR illuminator

Image intensifier tube

Converts photons to electrons and back again

Thermal Imaging

LGB

TOW

TOW

Questions?